Method and apparatus for locating which zone and sector of a mobile communication system a mobile station is in

ABSTRACT

A location method and system for a mobile communication system having a plurality of zones and a plurality of sectors in each zone. The location method and system locate a zone and sector in a zone where a mobile station is located. In the location system a base station associated with each zone transmits a control channel signal and transmits a sector signal for each sector in the zone. Each control signal of a zone differs from control channel signals of other zones. Each sector signal differs from other sector signal and control channel signals. A mobile station controller associated with each mobile station receives the control channel signals, determines which zone the mobile station is in as a location zone based on the received control channel signals, receives sector signals for sectors within the location zone, and determines which sector of the location zone the mobile station is in as a location sector based on the received sector signals.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention is applicable to mobile radio communication. Thisinvention relates, more particularly, to a method and apparatus fordeciding in which sector of a mobile communication system a mobilestation is in, where a radio zone (referred to as a zone herein) coveredby one base station is divided into several sectors in operation.

2. Description of the Related Art

In the prior art mobile communication system, a zone is divided intoplural sectors and each sector is covered by an antenna havingdirectivity. Such method is advantageous in that interferences betweensectors can be reduced by the directivity of the antennas, and thefrequency utilization efficiency is improved as the distance betweencells which are using the same frequency channels is shortened. In thistype of mobile communication system, it is necessary for a mobilestation to find out the serial number zone and of the sector in whichthe station is in at the time to set up a voice channel before the startof communication.

Even in the prior art mobile communication system where a zone is notdivided into sectors, a mobile station sometimes must decide in whichzone it is in. In the system where different zones are assigneddifferent frequencies respectively, a mobile station scans controlchannels assigned to the zones, and detects a zone in which the stationis in from the frequency (the serial number) of which control channelthe station could receive. Similarly, in a different prior art mobilecommunications system if a zone is divided into sectors, it is possiblefor a station to discriminate a sector by its frequency. In other words,sectors are assigned with control channels of different frequencies, anda mobile station decides in which sector it is in by detecting thefrequency or channel it can receive; or if a plurality of such channelsexists, by measuring receiving levels of these frequencies, comparingthem and discriminating the one with the maximum reception level.

However, in such a system of locating the sector in which one mobilestation is in from the sector frequency, as sectors are assigned with acontrol channel of different frequencies, the number of frequencies forcontrol channels is much larger than the number required for the systemin which control channels are assigned to different zones. For instance,if the zones are assigned with control channels of different frequenciesin the unit of nine zones, and the same frequency is repeatedly assignedto the next unit of nine zones or the 10th zone, then the number ofnecessary frequencies is nine. But if the sectors are assigned withdifferent frequencies, a zone is divided into six sectors, and the zonesare grouped in the unit of seven, 42 frequencies (6×7=42) will berequired for control channels as the same frequency is reassigned onlyto the 8th zone. Even if the system has a comparatively simple structureas above, the required number of control channels is as much as fivetimes more.

Moreover, the number of control channels which one mobile stationreceiver must scan for discriminating the sectors is large. Further, asit generally takes a certain amount of time to monitor the receivinglevel of a channel, the time required from activation of the powerswitch of a mobile station to when communication is ready with a set upcontrol channel becomes inconveniently long.

In the above conventional system, moreover, when one mobile stationmoves across the boundary of sectors, the number of frequencies it mustscan in order to detect the next control channel is so large that thestation takes much time for detection and control of movement betweensectors to conduct switching between the control channels smoothly. Asthe mobile station moves further during the delay in detection andcontrol, the receiving strength becomes lower than the marginal level atwhich a mobile station could receive control signals. Occasionally,switching of control channels becomes inoperable. Because one controlchannel can only cover a narrow area in such a system, the frequency ofchannel switching increases, and the possibility of not receiving thepaging signals during such channel switching increases proportionally.Due to the above reasons, reliability of receiving the paging signalsand channel switching control is deteriorated.

In such a system, the same information is often transmitted to all thesectors such as in the case of paging. In such a case, efficiency inutilization of frequency is low as the sectors must be assigned withdifferent frequencies.

In order to overcome the defects of the system where sectors areassigned with different control channels, there has been proposed apractical system where each zone is assigned with control channels ofthe same frequency. However, the system cannot rely on theaforementioned method to locate a sector where a mobile station existssimply by scanning the frequencies of control channels and detecting thefrequency with the maximum receiving level. Instead, a base stationmeasures an upward control channel signal issued from a mobile stationand compares with other signals to locate the relevant sector. (Thesignal generated by a mobile station for a base station is called anupward signal while the one generated from the base station for mobilestations is called a downward signal). In these systems where locatingof a sector should be done on the side of the base station, when amobile station turns on the power source at the start, or when the zonewhere it is in needs to be located, the station first scans thefrequencies of control channels assigned to different zones, measuresand compares the receiving levels thereof, discriminates the controlchannel frequency which has the maximum receiving level, and uses thefrequency of the upward control channel corresponding with thediscriminated frequency. When a mobile station receives or originates acall, as the mobile station uses an upward control channel to transmit asignal to the base station, the base station receives the upward signalby using an individual receiver allocated to each sector. The basestation measures and compares the levels at which each of the receiversreceives the signal, detects the sector in which the relevant mobilestation is in from the number of the individual receiver with themaximum level. In this system, the burden imposed on the base stationbecomes great as the individual receivers for the sectors of a zoneshould measure and compares the levels.

When an upward signal is received to measure its level, if the length ofthe signals generated from a mobile station is too short, it cannot bemeasured sufficiently. Due to the changes in level by fading, sectorssometimes cannot be precisely discriminated. In the system where the bittransfer speed of signals is set at a high rate, the signal lengthgenerally becomes short to deteriorate precision in sectordiscrimination. Poor precision in the sector discrimination means a highpossibility for connecting a wrong remote base station. In other words,the zones should be defined larger equivalently. This makes the distancewhich permits reassignment of the same frequency longer, the frequencyutilization efficiency lower, and the capacity of subscribers of thewhole system incapable of extension.

SUMMARY OF THE INVENTION

This invention solves such problematic aspects of the prior art, andprovides a system and method wherein a base station can be built withsimple facilities without requiring measurement and comparison oflevels. This invention further provides a system where the frequencyutilization efficiency is high. This invention provide a system whichhas a high precision in sector discrimination. This invention provides asystem of locating a sector where a mobile station exists with a higherreliability of paging signal reception.

This invention relates to a decision method and apparatus for locating asector in which a mobile station exists, comprising plural mobilestations including transmitter/receivers thereof, and a base stationwhich includes transmitter/receivers for communicating with pluralmobile stations, wherein each of the plural zones is divided intosectors, said transmitter/receivers of the base station include a firsttransmitter/receiver means which transmits/receives signals offrequencies including the control channels assigned to each of saidzones via a directive antenna, said each mobile stationtransmitter/receiver includes a second transmitter/receiver means whichtransmits/receives signals of frequencies including said controlchannels. The system of this invention is characterized in that saidfirst transmitter/receiver means further comprises a transmitter meanswhich transmits the signals of the sector individual frequenciesassigned to different sectors via each directive antenna, said secondtransmitter/receiver means includes a receiver means which receivessignals of the individual frequency of said each sector, a measuringmeans which measures the receiving level of the signals of theindividual frequency of each sector and the signal of the frequencyincluding each control channel, and a decision means which discriminatesthe zone and sector where the particular mobile station exists based onthe result of the measurement.

The second transmitter/receiver means according to this invention isstructured preferably with a detector means which compares the ratio ofthe receiving levels of signals of the individual frequency of a sectordetected by said decision means as the sector where the station ispresent against the signal of the frequency of control channel of thusdetected zone with a predetermined threshold value, and detects movementthereof between the sectors within the zone.

The transmitter means at the base station transmits signals of sectorindividual frequencies each allocated to a sector via a directiveantenna. The receiver of a mobile station receives the output signalfrom said means while the measuring means measures the receiving levelsof the signal of each sector individual frequency and of the signal ofthe frequency including each control channel. The decision means of themobile station detects the own zone and sector of the station based onthe frequency including the control channel with a higher receivinglevel and the sector individual frequency. With the above functions, thesystem can improve the frequency utilization efficiency, sectordiscrimination precision and paging signal reception reliability withoutthe need to execute level measuring and comparing on the side of thebase station. The same station can reduce the number of frequencieswhich the station should monitor by using the ratio in the receivinglevels of the signal of the sector individual frequency and of thesignal of the frequency which includes the control channel of the zonefor detection of the movement between the sectors within the zone tothereby shorten the time required for detecting the movement and improvethe intermittent ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a base station transmitter/receiver of thefirst embodiment of the decision method for locating a sector of amobile station according to this invention.

FIG. 2 is a block diagram of a mobile station transmitter/receiver ofthe first embodiment of the decision method for locating a sector of amobile station according to this invention.

FIG. 3 is a structural view of a control channel and sector individualfrequency of the decision method for locating a sector of a mobilestation according to this invention.

FIGS. 4a and 4b are frame formats of a control channel of the decisionmethod for locating a sector of a mobile station according to thisinvention.

FIG. 5 is a view to show the movement between zones of the decisionmethod for locating a sector of- a mobile station according to thisinvention.

FIG. 6 is a view to show the movement between sectors within a zone ofthe decision method for locating a zone of a mobile station according tothis invention.

FIGS. 7a and 7b are views to show the sectors adjacent to the sectorwhere a mobile station exists of the decision method for locating asector of a mobile station according to this invention.

FIG. 8 is a flow chart of the operation to detect the movement betweensectors in a zone of the decision method for locating a sector of amobile station according to this invention.

FIG. 9 is a view to show the arrangement of zones and sectors of thedecision method for locating a sector of a mobile station.

FIGS. 10a and 10b are formats of voice channel of the decision methodfor locating a sector of a mobile station according to this invention.

FIG. 11 is a view to show another arrangement of zones and sectors ofthe decision method for locating a sector of a mobile station.

FIG. 12 is a frame format of broadcasting information of a base stationof the decision method for locating a sector of a mobile stationaccording to this invention.

FIG. 13 is a flow chart of the operation to obtain the control channelsof the adjacent zones and individual frequencies of the adjacent sectorsbased on the broadcasting information from the base station of thedecision method for locating a sector of a mobile station according tothis invention.

FIG. 14 is a frame format of broadcasting information of another basestation of the decision method for locating a sector of a mobile stationaccording to this invention.

FIG. 15 is a chart to show correspondence between the order ofidentification numbers of sector individual frequencies broadcast from abase station of the decision method for locating a sector of a mobilestation according to this invention.

FIG. 16 is a flow chart of the operation which detects the individualfrequencies of adjacent sectors from the broadcast sector individualfrequency of the decision method for locating a sector of a mobilestation according to this invention.

FIG. 17 is a view to show an irregular zone/sector arrangement of thedecision method for locating a sector of a mobile station according tothis invention.

FIG. 18 is a flow chart of the operation which detects adjacent sectorindividual frequencies of the other zones from the broadcast informationof the decision method for locating a sector of a mobile stationaccording to this invention.

FIG. 19 is a flow chart to obtain zone control channels of adjacentsectors of another zone from broadcasting information of the decisionmethod for locating a sector of a mobile station according to thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention will now be described by referring to embodiments shownin the attached drawings. FIG. 1 is a block diagram of an embodiment ofthe base station transmitter/receiver of the decision method forlocating a sector of a mobile station according to this invention. FIG.2 is a block diagram to show an embodiment of a mobile stationtransmitter/receiver of the decision method for locating a sector of amobile station according to this invention. From FIG. 3, the relationbetween a zone and sectors will be easily understood.

Referring now to FIGS. 1 and 2, the system includes plural mobilestations having transmitter/receivers, a base station having atransmitter/receiver to communicate with said mobile stations, and zoneseach of which is further divided into sectors. The transmitter/receiverof the base station includes a first transmitter/receiver means 200which transmits or receives signals of the frequency f₀ including acontrol channel which is assigned to each of

the zones via directive antennas A₁ through A₆. The transmitter/receiverof each mobile station comprises a second transmitter/receiver means 100which transmits/receives signals of the frequency f₀ including thecontrol channel and an antenna 180. The second transmitter/receivermeans 100 comprises a demodulator 110, a band pass filter 120, afrequency converter 130, a control unit 150 and a part of a synthesizer170.

This invention system is characterized in that said firsttransmitter/receiver means 200 includes transmitter means whichtransmits signals f₁ through f₆ of sector individual frequenciesassigned to respective sectors via directive antennas A₁ through A₆. Thesecond transmitter/receiver means 100 includes a receiver means whichreceives signals f₁ through f₆ of said sector individual frequencies, alevel measuring circuit 140 as a measuring means which measures thereceiving levels of the signals of sector individual frequencies and ofthe signals of the frequencies of the control channels, a part of thecontrol unit 150 and a frequency memory 160 as the means for decidingwhich discriminates the zone and sector for the station based on theresult of the measurement by the circuit 140.

The decision method for locating a sector of a mobile station will nowbe described in respect of the operation. FIG. 3 is a structural view toshow the relation of control channels and sector individual frequenciesof this invention system. FIGS. 4a and 4b are frame formats of theinvention system. FIG. 5 is a view to show the movement between zones ofthis invention system. FIG. 6 is a view to show the movement betweensectors of a zone in which a mobile station exists. FIGS. 7a and 7b areviews to show sectors adjacent to the sector in which a mobile stationstays according to the present invention. FIG. 8 is a flow chart to showthe operation for detecting movement of a station between sectors of azone according to this invention system. FIG. 9 is a chart to show azone/sector arrangement of this invention system. FIGS. 10a and 10b areformats of voice channel of this invention system. FIG. 11 is a view toshow another zone/sector arrangement of this invention system. FIG. 12is a frame format of broadcasting information from the base stationthereof, FIG. 13 is a flow chart of the operation for detecting thecontrol channels of adjacent zones and adjacent sector individualfrequencies based on the broadcasting information thereof, and FIG. 14is a frame format of still another broadcasting information from thebase station thereof. FIG. 15 is a chart to show correspondence betweenthe order of identification numbers of the sector individual frequencieswhich is broadcast from the base station and the sector arrangements ofthe system, FIG. 16 is a flow chart for obtaining the individualfrequencies of sectors adjacent to the sector where the mobile stationstays out of the informed sector individual frequencies, FIG. 17 is aview to show the irregular zone and sector arrangement of this inventionsystem, and FIG. 18 is a flow chart to obtain individual frequencies ofadjacent sectors in other zones out of the broadcasting information ofthis invention system. FIG. 19 is a flow chart to obtain controlchannels of the adjacent sectors in other zones in the system thereof.

Table 1 shows correspondence between the zones and the control channelsof this invention system, Table 2 correspondence of the sectors and thesector individual frequencies, Table 3 the content of non-volatilememory of the mobile station transmitter/receiver, and Table 4correspondence between the frequencies which a mobile station shouldstore and the identification numbers thereof in a system where a basestation broadcasts the sector individual frequencies of the system.Table 5 shows correspondence between the order of broadcasting from thebase station and the identification numbers of the system, and Table 6shows tables which the base station broadcasts to mobile stations in thesystem according to this invention.

In FIG. 3, f₁₀ , f₂₀ , f₃₀ , f₄₀ , f₅₀ , f₆₀ , and f₇₀ denotefrequencies of the control channels assigned to respective zones. InFIG. 3 f₁₁ -f₁₆, f₂₁ -f₂₆, . . . , f₇₁ -f₇₆ denote the sector individualfrequencies which are constantly transmitted from the base station. FIG.1 shows a structure where a zone is divided into six sectors whereineach of the antennas A₁ through A₆ is allocated to each sector. AntennasA₁ through A₆ are respectively connected to transmitter/receivers of thefrequency F₀ of the control channel of the zone, the sector individualfrequencies f₁,f₂, f₃,f₄, f₅, f₆ and voice channels of the sectors.Although the system shown in FIG. 1 is structured to have thetransmitter/receivers for the frequencies f₀ of control channels in thenumber corresponding to that of sectors, signals from onetransmitter/receiver may be distributed to the power supply sections ofsectors.

In FIG. 2, the level measuring circuit 140 is the circuit for measuringthe receiving levels of the signal frequencies, the synthesizer 170 iscontrolled by the controller 150, and the frequencies are selected bythe converter 130 and the band pass filter 120.

When a power switch is turned on, a mobile station scans controlchannels assigned to zones to measure the receiving levels and comparethem. In minimizing errors due to fading, it is more effective to switchto a high speed and repeat short measuring cycles for plural times perfrequency rather than to measure levels of a frequency once. Thescanning time may be shortened by omitting the frequencies with thelevels which are formed extraordinarily low by the first measurement.From the result of scanning, the control channel with the strongestreceiving level is judged as the zone in which the particular mobilestation is in.

The mobile station scans the sector individual frequencies of the zonewhen the receiving channel of the control channel is not used, measuresthe receiving levels and compares them in order to render sectorjudgement. It is quite obvious from FIG. 4(a) that a control channel hasblank sections not used for reception. The letter X in FIG. 4(a) denotesa broadcasting section and Y a paging section. As the paging section isdivided into subsections and a mobile station receives paginginformation only of a sub-section to which it belongs, the station doesnot have to receive control channels of the zone of the paging sectionsof other sub-sections. This produces blank time and permits receivingother frequencies. In the FIG. 4(b), shaded sections denote blank timesof the paging section Y of the group of the mobile stations. Becausethere are blank times in the control channels for receiving, the mobilestation can receive and at the same time measure the sector individualfrequencies and judge that the sector having the sector individualfrequency with the strongest receiving level is the sector in which thestation exists.

Operation is described for the zone/sector discrimination for the timeof turning on the switch referring to the case of FIG. 4 where controlchannels are structured to repeat the same frequency in the unit ofseven zones. It is assumed that the sector in which the particularmobile station stays is the sector having the individual frequency off₇₃. The mobile station first scans the control channels f₁₀ , f₂₀ ,..., f₇₀. Then, it scans the sector individual frequencies f₇₁, f₇₂, . .. , f₇₆ of the zone of which control channel is f₇₀ and judges that thesector where the station stays is f₇₃.

After judging the sector for activation, the mobile station advances tothe state of waiting for paging. While waiting, the mobile station isconstantly moving, the movement thereof between the sectors and thezones are monitored. The mobile station can learn its movement betweenzones by monitoring control channels which are assigned to zonesrespectively in one-to-one relation, and learn movement between sectorsin the zone by monitoring the sector individual frequencies. Forinstance, when a mobile station moves as shown in FIG. 5, as the controlchannel having the strongest receiving level moves from the zone Z1 tothe zone Z2, the station can learn that it has moved from the zone Z1 tothe zone Z2. In the case where a station moves from one sector toanother sector of the same zone, as shown in FIG. 6, the strongestreceiving level changes from the sector individual frequency of thesector S1 of the six sectors of the zone to that of the sector S2, andit becomes obvious that the station moves from the sector S1 to thesector S2. Although the movement between the cells is learned bymonitoring the control channels in the above example, the movementbetween both sectors and zones in the waiting state may be learned bymonitoring the sector individual frequencies alone. It may be learned bymeasuring and comparing the receiving levels of individual frequenciesof sectors adjacent to the sector where the mobile station existsirrespective of zones. As shown in FIG. 7a, if it is assumed that thestation is in a sector S1, the station measures and compares thereceiving levels of the individual frequencies of adjacent sectors, thesectors S2 through S6 of the same zone and the sectors S7 through S10 ofother zones where the station can possibly move to. If the receivinglevels are strong in the sectors S2 through S6, it is judged that thestation moves within the zone. On the other hand, if they are strong inthe sectors of S7 through S10, it is judged that the station moves toanother zone. As shown in FIG. 7b the control channels at the zones canoverlap somewhat.

If the number of sector individual frequencies is reduced, it mayshorten the detecting time of the movement. The reduction of the numberof sector individual frequencies means an increase in time where noreception is being made, or an improvement of intermittent ratio. Inother words, it saves consumption power of a mobile station, especiallyof a portable unit, prolongs the life of a battery, and improves thequantity of service. A scan of only the sectors of higher probability tomove to can be performed and then, if necessary, to scan other sectorsof lower possibility rather than to scan all of the adjacent sectors.For instance, in the case shown in FIG. 7a, if the mobile station staysin the sector S1, the sectors of S2, S6, S8 and S9 which contactlinearly with the sector S1 are scanned first. If any higher receivinglevel is not obtained even after scanning them, then other sectors arescanned as the station may have moved to others. In this method, thenumber of sectors which are monitored is 4. Compared to the method whereall the sectors including those contacting the sectors 1 with points aremonitored, the number decreased from 10 to 4 or less than a half tothereby save time. The method of scanning from the sector of higherprobability may be used for monitoring the control channels. The numberof scanning may be reduced if the monitoring of a control channel of azone having a higher probability in movement is preferentially scanned.

The above mentioned monitoring of the movements between the zones andsectors is the method of scanning the frequencies of adjacent zones,comparing them and discriminating the frequency with the strongestreceiving level as the frequency of the zone or sector where aparticular mobile station exists. However, the movement between thesectors in a zone may be monitored by another method. Instead ofconstantly monitoring individual frequencies of the adjacent sectors ofthe zone, the method usually monitors only[the individual frequency ofthe sector where the station exists]/[control channel of the zone inwhich the station exists]. As the control channels are of the samefrequency for all of the sectors of the zone, there is hardly anydirectivity in the level distribution thereof. But the sector individualfrequency differs from one sector to another and has directivity; inother words, the receiving level may be strong in one sector but weak inanother. As (the individual frequency of the sector where a stationexists)/(control channel of the zone where the station exists) is closeto 1 in the sector where the station is in and is close to 0 in othersectors, when a mobile station moves across the boundary between the twosectors, the ratio of the individual frequency of the sector as againstthe control channel of the zone where it stays decreases and the mobilestation can learn from the decrease that it moves from one sector toanother within the same zone. After moving out of the sector, the mobilestation measures and compares the frequency of the sector adjacent tothe former one or the one it moves into, and judges into which sector itmoves.

This method is advantageous as it can shorten the time for detecting andimprove the intermittent ratio as it usually must monitor only the ratioof the individual frequency of its own sector against the controlchannel of the zone thereof. FIG. 8 shows the flow chart of theoperation wherein the above method is applied to monitoring of themovement between the sectors of a zone. In the operation shown in FIG.8, in addition to the aforementioned monitoring, the monitoring ofcontrol channels of adjacent zones is used in order to detect themovement between the zones. In FIG. 8, the relation holds as;

    Function L (f.sub.i)=(measured value of the receiving level of the frequency f.sub.i)

The symbols α and β denote constants. The zone/sector arrangement isshown in FIG. 9, and the control channels and the individual frequenciesare assigned as shown in Table 1. The zone and the sector where theparticular mobile station stays are Z0 and A respectively. The symbolsused in relation to FIG. 9 such as Z0, Z1, Z2 or A, B, C, ... arerelative symbols for the zone or sector where the station exists andwill be changed when the station moves. As is obvious from FIG. 8, amobile station measures the control channel of the zone f₀ where it isin and control channels f₀ ' and f₀ " of the adjacent zones and detectsthe movement between the zones. When the station finds that it has notmoved between the zones, it measures the sector individual frequencyf_(A), detects the ratio of f_(A) /f₀ and monitors the movement betweenthe sectors. If the ratio f_(A) /f₀ becomes lower than a certain valueβ, the station is likely to have moved from one sector to another. Thereceiving levels of the individual frequencies of sectors of the samezone, f_(B), f_(C), f_(D), f_(E), f_(F), are measured and compared, andthe sector having the individual frequency with the highest receivinglevel is judged to be the sector to which the station has moved. If thevalue β is set high, as it scans the individual frequencies of sectorswithin the same zone faster when the station moved between sectors, theintermittent ratio decreases while judgement becomes easier. The value βmay be set considering the tradeoff between the intermittent ratio andjudgement precision.

The foregoing explanation has been given to the case of judging a zoneand a sector when the power is turned on or during waiting, but thissystem may be applied to the zone/sector decision during a voicecommunication. In such a case, a method which switches to anotherfrequency in a time slot other than the communication slot by using TDMA(time division multiplex access method) or a method wherein a receiverfor level monitoring is installed at a mobile station should be applied.The communication channels at TDMA may be structured as shown in FIGS.10a and 10b wherein the slot used for the communication is a part of theTDMA frames. A zone or sector may be judged as in the waiting time byusing the blank time as such blank times are produced when not receivingthe voice channels. The letters ST in FIG. 10(a) denote a slot used forthe communication while the shaded portions in FIG. 10(b) denote blanktimes.

As the above mentioned sector decision method according to thisinvention does not require measurement nor comparison of receivinglevels on the side of the base station, the burden on the base stationis not heavy since the control channels and the sector individualfrequencies of a mobile station are measured and compared in thereceiving levels. As the sector individual frequencies are constantlytransmitted, a mobile station can receive signals of a sufficient lengthand measure the receiving levels for a sufficient time to thereby enableprecise decision of a sector.

As the control channels are assigned to zones rather than sectors, thefrequency utilization efficiency of the channels is quite high.

Compared to the case wherein control channels are assigned to sectors,the number of scans for the frequencies during the time from switchingon to the sector decision and the number of scans of the frequencieswhen movement is judged are smaller to thereby minimize the timerequired to judge the sector. For instance, if channels are assigned tosectors respectively and sectors are grouped in the unit of six andrepeated in the unit of seven zones, the number of scans for the controlchannels is 6×7=42. According to the method of the present inventionwherein the same frequency is reassigned in the unit of nine zones, thecontrol channels are scanned for nine times and sector individualfrequencies are scanned for six times to total 15; (9+6=15). Therefore asector can be decided within about one third of the conventionallyrequired time.

In the system according to this invention, the number of the frequencieswhich should be scanned before a control channel is detected and thestate becomes ready for paging is nine. If control channels are assigneddifferently to sectors, the number of frequencies scanned is 42. Thesystem of the present invention becomes therefore "ready state" withinabout one fifth of the time conventionally needed. The time needed forturning on to the ready state is shortened, and the time needed fromswitching the control channel for the different zone and preparing forthe ready state is also reduced. Further, as control channels areassigned to zones and as the same control channel is used within a zone,the control channels do not need to be switched from one to the otherfor movement between the sectors in a zone. This makes paging possibleeven if the decision of a sector is delayed or erroneously made.

The first embodiment for a mobile station to learn the sector individualfrequency is the method in which the sector individual frequency storedby the station in a non-volatile memory. Table 3 shows the structure ofthe contents stored in a memory. The letters f₁₀ -f₇₀ denote frequenciesof the control channels assigned to zones (or cells. The letters f₁₁-f₁₆, . . . , f₇₁ -f₇₆ denote sector individual frequencies. If thearrangement of the zones and sectors is regular, it is possible to learnthe control channels and individual frequencies of adjacent zones andsectors out of the information stored in the non-volatile memory.

The second embodiment for a mobile station to learn the sectorindividual frequencies is the method in which a base station informs thesector individual frequencies to mobile stations. Alternatively, thismethod may be used for the control channels so that the base stationinforms the control channels of the zones adjacent to the zone where themobile station is in. The method is advantageous as it can be flexiblyused even if the arrangement of the zones/sectors is irregular when itshould obtain the control channels of adjacent zones or the individualfrequencies of the adjacent sectors. However, the amount of broadcastinginformation increases compared with the case where mobile stations storethe information in memories, and it is preferable to reduce the amountof information. For this purpose, it is preferable to prepare a tablewhich relates frequencies with identification numbers like Table 4inside the mobile stations and broadcasting should be made with the IDnumbers rather than frequencies. The content of broadcast informationmay be only the sector individual frequencies of a zone or theindividual frequencies of the sectors of a zone where a mobile stationexists and of the sectors adjacent thereto depending on the monitormethod for the movement thereof. The number of control channels whichare to be monitored may be reduced by informing not only the sectorindividual frequencies but also the control channels of the adjacentzones.

As an example of the case wherein a base station broadcasts to mobilestations the frequencies to be monitored, the base station informs thesector individual frequencies in the zone where it is in and the controlchannels of adjacent zones. Referring to FIG. 11 where the station is inthe zone Z0, the control channel of the zone informs the individualfrequencies of the sectors A through F of the zone and the controlchannels of the zones which are adjacent to the sectors as shown in FIG.12. In FIG. 12, the parts marked with the letters A, . . . , F are theparts in which the sector individual frequencies of the sectors Athrough F will be informed and those marked with Z1 through Z8 are theparts in which the control channels of the zones Z1 through Z8 will beinformed. 0 and 1 denote the bits for identifying the sector individualfrequencies from the zone control channels. If it is assumed that thesectors F, A, B, and zones Z8, Z1, Z2, Z3 should be monitored while themobile station is within the sector A, the mobile station will obtainthem from the broadcasting information in accordance with the operationflow shown in FIG. 13. It is assumed that the functions f and g have thevalues shown in FIG. 12.

In FIG. 14 is shown another example of the broadcasting informationstructure where the sector individual frequencies of the zone whereinthe mobile station is in and the control channels of adjacent zonesshould be informed. In FIG. 14, the letter V denotes parts in which thesector individual frequencies should be informed while W denote theparts in which the control channels of the zones adjacent thereto shouldbe informed. For instance, if a mobile station is within the sector A inFIG. 11, the mobile station receives the part of the sector A of thesector individual broadcasting part V to learn its own individualfrequency. Then, the station reads out the part of the sector A of thepart W the adjacent zone control channels' broadcasting information tolearn the control channels of the zones adjacent to its own zone are forZ8, Z1, Z2 and Z3. This method can improve the intermittent ratio as themobile station of the sector A must receive the broadcasting informationaimed at the sector A alone.

An example will be shown below for the case where both of the individualfrequencies of the sectors of the zone in which the station exists andof the adjacent zones are broadcast. This method broadcasts to themobile station the aforementioned information by arranging theidentification numbers for the sector individual frequencies in an ordershown in FIG. 15 and Table 5. FIG. 15 shows correspondence between theorder of ID numbers of the sector individual frequencies to be informedand the sector arrangement while Table 5 shows correspondence betweenthe order and the ID numbers. FIG. 16 shows in flow chart the method toobtain the sector in which a mobile station exists and its adjacentsectors by means of the table which is informed by the base station. Forexample, if the mobile station is in the sector of the order 1, adjacentsectors of the other zones will be the sectors of the order 18, 7, 8 and9 from FIG. 16.

The method mentioned may be used for the case where the arrangement ofzones and sectors is irregular. The method is exemplified below whereinthe control channels of the adjacent zones is informed. FIG. 17 shows anirregular case wherein the sectors within the same zone are identifiedwith letters A through F. In this case, the number of adjacent zones isseven and the number of adjacent sectors in the other zones whichcontact the zone B by line is six. This case is irregular compared tothe case shown in FIG. 15 where the number of adjacent zones is six andthe adjacent sectors of other zones is four. What the base stationshould inform are the ID number of the sector individual frequencies ofthe zone where the mobile station is in, the individual frequency IDnumbers of the sectors in other zones on which the sectors of its ownzone contact, and the control channels of the contacting sections of theother zones. The base station first of all informs the ID numbers of thesector individual frequencies of the zone where the mobile station isfrom the sectors A to F as shown in the first table or Table 6(a) in thealphabetical order.

Then, the adjacent sectors of the other zones correspond with thesectors of the zone where the mobile station stays. It prioritizes thesector which contacts with the other sector(s) most. For instance, asthe sector S4 contacts only with the sector B, it is judged that itcorresponds to the sector B. If a sector contacts with plural sectorslike the sector S8 with the sectors B and C, the sector C is prioritizedas it contacts with the sector S8 in a larger area, and judged tocorrespond with the sector S8. Then, the base station informs the numberof adjacent sectors in other zones corresponding to the sectors Athrough F in the alphabetical order like Table 6(c).

Then, it informs the ID number of the adjacent sector individualfrequencies of other zones corresponding to the sectors A through F inthe order of the number in FIG. 17 like sectors S1, S2, . . . , S15 asshown in Table 6(b) starting from the sector corresponding to the sectorA. The order is clockwise from the sector contacting with the Sector A.It also informs the control channels of the zones to which the sector S1belongs in the clockwise order as shown under the column of the adjacentsector individual frequencies in Table 6(b). The order of notificationis in the order of the zones numbered with I, II, . . . , VII in FIG.17. The data is read out from the Table 6(d) in order to learn the zonesto which the adjacent sectors belong. The table groups the sectors inthe unit of a zone and notifies the number of sectors of each zonestarting from the sector S1. In this case, as they are grouped in(Sector S1), (S2, S3), (S4, S5, S6), (S7, S8), (S9), (S10, S11, S12),(S13, S14), (S15), it informs like 1 , 2 , 3 , 2 , 1 , 3 , 2 , and 1 .

FIGS. 18 and 19 show the method to obtain the individual frequencies ofthe adjacent sectors of other zones contacting with the sector in whicha mobile station exists and the control channels of zones to which thesectors belong by means of the information of the broadcasting tables.In the figures, the function Fa is defined as follows.

    Fa(A)=1, Fa(B)=2, . . . , Fa(F)=6.

The letter T₂ (i) denotes the values which belong to the order i in thesecond table, T₃ (i) the values which belong to the order (i) of thethird table and T₄ the values which belong to the order (i) in thefourth table. ##EQU1## An identifier of EOT (end of table), for instancethe numeral 0, should be inserted in the end of the second table.

The broadcasting method mentioned above has been described so far onassumption that the base station does not know in which sector a mobilestation in question is in. The method is applicable to the time ofswitching on and in the waiting state. But after a communication isstarted and the base station has learned the sector where the mobilestation exists, the base station has to inform only the individualfrequencies of the adjacent sectors of the same zone and the controlchannels of the adjacent zones. During the waiting state, the mobilestation learns these frequencies from the broadcasting information inaccordance with a certain procedure, but during a communication, thebase station informs simply the frequencies as they are. A part of thecommunication channels may be used for the channels through which thebase station informs the mobile station of those frequencies during acommunication by means of frequency division multiplex or time divisionmultiplex. As communication channels are assigned to respective mobilestations during a communication, they can transmit information exclusiveto each station. Taking advantage of the feature, the broadcastingmethod is practically feasible.

Communication channels may be used for the sector individual frequenciesby assigning a certain predetermined channel to each sector and usingthe channel as the individual frequency for identifying the sector. Forthe purpose, the communication channels do not need to have any specialinformation in their content for sector identification but mustconstantly issue radio waves at their unique frequencies. If channelsare preferentially assigned to communication, almost no demerit will beproduced even if they have to constantly issue radio waves.

Alternately, carriers without modulation may be used as the sectorindividual frequencies. They need not to be modulated as they do nothave to transmit any information but are used simply to identify thereceiving levels for identification of sectors. As carriers withoutmodulation have almost no frequency band, they hardly impose extraburden on the other components even if their frequencies are utilized.

The sector individual frequencies may be the control channels whichtransmit the control signals for respective sectors or the frequenciesfor user packets.

This invention has been described referring to the case where a systemis divided into sectors, but this method is applicable to decide thezones in the system where plural base stations are used as a unit in thecontrol channel structure and assigned with individual frequenciesrespectively. The assignment of individual frequencies may be made inplural stages. More specifically, plural number of units to each ofwhich is assigned the individual frequency is grouped and then the groupis assigned with another individual frequency. By assigning them in twohierarchical stages, the number of scans for identification of theposition of a mobile station may be simplified as the individualfrequencies of the larger groups are first scanned and then those ofdownstream groups are sequentially scanned.

INDUSTRIAL USE

As described in the foregoing statement, this invention achieves a highutilization efficiency of the frequencies as one control channel isassigned to one zone instead of one sector. It is advantageous as itneeds not to measure the receiving levels at the base station andtherefore can reduce the burden imposed on the base station.

The method according to this invention can improve paging signalreception reliability and sector decision precision and shorten the timerequired from the activation to preparation of ready condition forpaging.

This invention method can reduce the number of frequencies which shouldbe monitored, shorten the time for detecting movement, and improve theintermittent ratio as it uses the measurement and comparison of relativevalues of the control channels of the zone in which a mobile stationstays and individual frequency of the sector it stays for detecting themovement within the zone.

This invention can reduce the number of frequencies which should bemonitored as the method for the base station informs mobile stations ofthe sector individual frequencies and the control channels of the zonemay be used to the irregular arrangement of zones and sectors to learnthe control channels of the adjacent zones and individual frequencies ofthe adjacent sectors.

                  TABLE 1                                                         ______________________________________                                               Zone Control channel                                                   ______________________________________                                               Z0   f.sub.0                                                                  Z1    f.sub.0 '                                                               Z2    f.sub.0 "                                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Sector      Control channel                                                   ______________________________________                                        A           f.sub.A                                                           B           f.sub.B                                                           C           f.sub.C                                                           D           f.sub.D                                                           E           f.sub.E                                                           F           f.sub.F                                                           ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Control channel                                                                            Sector individual frequency                                      ______________________________________                                        f.sub.10     f.sub.11, f.sub.12, f.sub.13, f.sub.14, f.sub.15, f.sub.16       f.sub.20     f.sub.21, f.sub.22, f.sub.23, f.sub.24, f.sub.25, f.sub.26       f.sub.30     f.sub.31, f.sub.32, f.sub.33, f.sub.34, f.sub.35, f.sub.36       f.sub.40     f.sub.41, f.sub.42, f.sub.43, f.sub.44, f.sub.45, f.sub.46       f.sub.50     f.sub.51, f.sub.52, f.sub.53, f.sub.54, f.sub.55, f.sub.56       f.sub.60     f.sub.61, f.sub.62, f.sub.63, f.sub.64, f.sub.65, f.sub.66       f.sub.70     f.sub.71, f.sub.72, f.sub.73, f.sub.74, f.sub.75,                ______________________________________                                                     f.sub.76                                                     

                  TABLE 4                                                         ______________________________________                                        ID number     Frequency                                                       ______________________________________                                         1            f.sub.1                                                          2            f.sub.2                                                          .            .                                                                .            .                                                                .            .                                                               255           .sup.  f.sub.255                                                256           .sup.  f.sub.256                                                ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Order    ID number     Order   ID number                                      ______________________________________                                        1        37            10      18                                             2        38            11      17                                             3        39            12      19                                             4        40            13      24                                             5        41            14      26                                             6        42            15      25                                             7         3            16      33                                             8        11            17      32                                             9        10            18       4                                             ______________________________________                                    

                  TABLE 6(a) TABLE 1                                              ______________________________________                                        Order   ID number              Sector                                         ______________________________________                                        1       43              . . .  A                                              2       44              . . .  B                                              3       45              . . .  C                                              4       46              . . .  D                                              5       47              . . .  E                                              6       48              . . .  F                                              ______________________________________                                    

                  TABLE 6(b) TABLE 2                                              ______________________________________                                                       Order ID number                                                ______________________________________                                        Sector individual                                                                              1        3                                                   frequency in other                                                                             2        4                                                   zone             3        12                                                                   4        11                                                                   5        10                                                                   6        13                                                                   7        18                                                                   8        19                                                                   9        26                                                                   10       25                                                                   11       30                                                                   12       32                                                                   13       31                                                                   14       38                                                                   15       39                                                  Zone control     16      202                                                  channel          17      205                                                                   18      208                                                                   19      207                                                                   20      206                                                                   21      203                                                                   22      201                                                                   23      EOT                                                  ______________________________________                                                Sector                                                                              Zone                                                            ______________________________________                                                      I                                                                       A                                                                                   II                                                                      B     III                                                                           IV                                                                      C                                                                                   V                                                                       D                                                                                   VI                                                                      E                                                                                   VII                                                                     F                                                                                   I                                                               ______________________________________                                    

                  TABLE 6(c) TABLE 3                                              ______________________________________                                        Order    ID number              Sector                                        ______________________________________                                        1        3               . . .  A                                             2        4               . . .  B                                             3        1               . . .  C                                             4        3               . . .  D                                             5        2               . . .  E                                             6        2               . . .  F                                             ______________________________________                                    

                  TABLE 6(d) TABLE 4                                              ______________________________________                                        Order    ID number              Sector                                        ______________________________________                                        1        1               . . .  Z1                                            2        2               . . .  Z2                                            3        3               . . .  Z3                                            4        2               . . .  Z4                                            5        1               . . .  Z5                                            6        3               . . .  Z6                                            7        2               . . .  Z7                                            8        1               . . .  Z1                                            ______________________________________                                    

What is claimed is:
 1. A location system for a mobile communicationsystem having a plurality of zones and a plurality of sectors in eachzone, the location system locating a particular zone and sector in whicha mobile station is located, the location system comprising:a basestation means associated with each zone for transmitting a controlchannel signal for its associated zone, each zone's control channelsignal being different from those of other zones, and for transmitting asector signal for each sector in the zone, each sector signal beingdifferent from other sector signals and control channel signals; andmobile station means associated with each mobile station for receivingcontrol channel signals, determining which zone the mobile station is ina location zone based on the received control channel signals, receivingsector signals for sectors within the location zone, and determiningwhich sector of the location zone the mobile station is in a locationsector based on the received sector signals.
 2. The location system ofclaim 1, wherein the base station means comprises basetransmitter/receiver means for transmitting the control channel signaland a sector signals via directional antennas, each directional antennabeing associated with a sector, the base transmitter/receiver meanstransmitting the control channel signal via the directional antennas andtransmitting each sector signal via a corresponding directional antenna.3. The location system of claim 1, wherein the mobile station meanscomprises:mobile transmitter/receiver means for receiving signalsincluding the control channel signals and sector signals; filter meansfor selecting a received signal; measuring means for measuring thereceiving level of the selected received signal; control means forcontrolling the filter means to select the received control channelsignals, determining as the location zone a zone associated with acontrol channel signal having the highest receiving level, controllingthe filter means to select the sector signals associated with thesectors in the location zone, and determining as the location sector asector associated with a sector signal having the highest receivinglevel.
 4. The location system of claim 3, wherein the mobile stationmeans comprises:a frequency memory means for storing frequencies of thecontrol channel signals and frequencies of the sector signals associatedwith each control channel signal; wherein the filter means selects areceived signal based on a desired frequency output by the controlmeans; and the control means inputs the frequencies of the controlchannel signals from the frequency memory means, outputs the frequenciesof the control channel signals to the filter means as desiredfrequencies, inputs the frequencies of the sector signals associatedwith the sectors in the location zone from the frequency memory means,and outputs the frequencies of the sector signals associated with thesectors in the location zone to the filter means as desired frequencies.5. The location system of claim 3, whereinthe base station meanstransmits identification signals indicating frequencies of the controlchannel signals and indicating frequencies of the sector signalsassociated with the sectors of each zone; and the filter means selects areceived signal based on a desired frequency output by the controlmeans; and the control means controls the filter means to select theidentification signals, determines the frequencies of the controlchannels signals from the identification signals, outputs thefrequencies of the control channel signals to the filter means asdesired frequencies, determines the frequencies of the sector signalsassociated with sectors in the location zone based on the identificationsignals, and outputs the frequencies of the sector signals associatedwith the sectors in the location zone to the filter means as desiredfrequencies.
 6. The location system of claim 5, whereinthe mobilestation means further comprises frequency memory means for storing thefrequencies of the control channel signals and the frequencies of thesector signals, the stored frequencies being addressable based on acorresponding identification address; wherein the base station meanstransmits the identification signals each indicating a differentidentification address; and the control means inputs the frequencies ofthe control channels and the sector signals associated with the sectorsin the location zone from the frequency memory means using theidentification addresses.
 7. The location system of claim 1, wherein themobile station means further performs the function of detecting movementof the mobile station from one sector to another within a zone.
 8. Thelocation system of claim 7, wherein the mobile station means furthercomprises:mobile transmitter/receiver means for receiving signalsincluding the control channel signals and the sector signals; filtermeans for selecting a received signal; measuring means for measuring thereceiving level of the selected received signal; control means forcontrolling the filter means to select the control channel signalassociated with the location zone and the sector signal associated withthe location sector, determining a ratio of a receiving level of thesector signal associated with the location sector to a receiving levelof the control channel signal associated with the location zone,comparing the ratio to a predetermined value, and determining that themobile station has moved to a new sector based on the comparison.
 9. Thelocation system of claim 1, wherein the mobile station means furtherperforms the function of detecting movement of the mobile station fromone zone to another.
 10. The location system of claim 9, wherein themobile station means comprises:mobile transmitter/receiver means forreceiving signals including the control channel signals and the sectorsignals; filter means for selecting a received signal; measuring meansfor measuring the receiving level of the selected received signal;control means for controlling the filter means to select the controlchannel signal associated with the location zone and control channelsignals associated with zones adjacent to the location zone, determininga ratio of a receiving level of a control channel signal associated withan adjacent zone to a receiving level of the control channel signalassociated with the location zone, comparing the ratio to apredetermined value, and determining that the mobile station has movedto the adjacent zone based on the comparison.
 11. The location system ofclaim 10, wherein the mobile station mean comprises memory means forstoring which zones are adjacent to each zone and control channelsignals thereof, and the control means inputs from the memory meanscontrol channel signals of zones adjacent to the location zone.
 12. Thelocation system of claim 10, wherein the base station means transmitsidentification signals indicating that zones are adjacent to each zoneand control channel signals thereof, and the control means determinescontrol channel signals of zones adjacent to the location zone based onthe identification signals.
 13. A location method for a mobilecommunication system having a plurality of zones and a plurality ofsectors within each zone, the location method locating which zone andsector within the zone a mobile station is in, each zone associated witha base station, each base station transmitting signals including acontrol channel signal and sector signals, each control channel signaldiffering from control channel signals of other zones, and each sectorsignal being associated with a sector in a zone and differing rom othersector signals and control channel signals, the method comprising thesteps of:receiving signals on a mobile station's transmitter/receiverincluding control channel signals and sector signals; first measuring areceiving level of each control channel signal using a receiving leveldetector of the mobile station; first determining which zone the mobilestation is in as a location zone based on the receiving levels of thecontrol channel signals using a controller of the mobile station; secondmeasuring a receiving level of each sector signal associated with thesectors in the location zone using the receiving level detector; andsecond determining which sector of the location zone the mobile stationis in as a location sector based on the receiving levels of the sectorsignals associated with the sectors in the location zone using thecontroller of the mobile station.
 14. The location method of claim 13,whereinthe first measuring step includes the steps of:first filteringthe received signals to obtain each control channel signal using afilter means of the mobile station, and first detecting the receivinglevel of each obtained control channel signal using the receiving leveldetector of the mobile station; and the second measuring step includesthe steps of:second filtering the received signals to obtain each sectorsignal of sectors in the location zone using a filter means of themobile station, and second detecting the receiving level of eachobtained sector signal associated with the sectors in the location zoneusing receiving level detector of the mobile station.
 15. The locationmethod of claim 13, whereinthe first determining step includes the stepsof determining which control channel signal has the highest receivinglevel, and designating the zone associated with the control channelsignal having the highest receiving level as the location zone; and thesecond determining step includes the steps of determining which sectorsignal of the sectors in the location zone has the highest receivinglevel, and designating the sector associated with the sector signalhaving the highest receiving level as the location sector.
 16. Thelocation method of claim 13, further comprising the steps of:thirddetermining a ratio of the receiving level of the sector signalassociated with the location sector to the receiving level of thecontrol channel signal associated with the location zone; comparing theratio to a predetermined value; and fourth determining that the mobilestation has moved to a new sector based on results of the comparisonstep.
 17. The location method of claim 13, further comprising the stepsof:determining a ratio of the receiving level of a control channelsignal associated with an adjacent zone to the receiving level of thecontrol channel signal associated with the location zone; comparing theratio to a predetermined value; determining that the mobile station hasmoved to a new zone based on the results of the comparison step.
 18. Alocation method for a mobile communication system having a plurality ofzones and a plurality of sectors in each zone, the location methodlocating which zone and sector within a zone a mobile station is in, themethod comprising the steps of:transmitting a control channel signal andsector signals for each zone from a corresponding base station, eachcontrol channel signal of a zone differing from control channel signalsof other zones, and each sector signal being associated with a sector ina zone and differing from other sector signals and control channelsignals; receiving signals on a mobile station's transmitter/receiverincluding control channel signals and sector signals; first measuring areceiving level of each control channel signal using a receiving leveldetector of the mobile station; first determining which zone the mobilestation is in as a location zone based on the receiving levels of thecontrol channel signals using a controller of the mobile station; secondmeasuring a receiving level of each sector signal associated with thesectors in the location zone using the receiving level detector; andsecond determining which sector of the location zone the mobile stationis in as a location sector based on the receiving levels of the sectorsignals associated with the sectors in the location zone using thecontroller of the mobile station.